1. Field of the Invention
The present invention relates to a wheel bearing device with a rotation detector for use in an automotive vehicle of a type equipped with an anti-lock brake system.
2. Description of the Related Art
In recent years, export of automobile component parts to BRIC countries, where the economic growth is taking place markedly, is increasing. Those automobile component parts so exported include a wheel support bearing assembly for rotatably supporting a vehicle wheel relative to a vehicle body structure, which assembly makes use of a wheel lock detecting sensor for the anti-lock brake system (ABS) of the automotive vehicle. This wheel lock detecting sensor is built in the wheel support bearing assembly and is generally in the form of a rotation detecting device made up of a magnetic encoder, which is quite often made of a magnetic rubber material, and a magnetic sensor element for detecting the rotation of the vehicle wheel with the magnetic encoder taken as a target.
Since in those BRIC countries, it is quite often that automobiles are driven on unpaved and tough roads, the magnetic encoder employed in the rotation detecting device is generally required to have a high wear resistance particularly where such rotation detecting device is assembled in the wheel support bearing assembly for automotive vehicles. For this reason, the magnetic encoder made of a magnetic rubber material by means of a heating and compressing process has hitherto been protected by a protective covering, made of a non-magnetic material and coated over the surface of the magnetic encoder, to minimize the accelerated wear.
It has, however, been found that the protection of the magnetic encoder surface with protective covering made of the non-magnetic material such as described above is accompanied by an increase in size of the gap present between the surface of the magnetic encoder and the magnetic sensor element disposed in face to face relation therewith, and, therefore, the magnetic encoder so manufactured tend to have an increased magnetic flux density.
To alleviate the problems and inconveniences inherent in the prior art magnetic encoder of the kind discussed above, the rotation detector equipped wheel support bearing assembly has been suggested, in which the magnetic encoder and the magnetic sensor element are arranged within a bearing unit. (See, for example, the Patent Document 1 listed below.)    [Patent Document 1] JP Laid-open Patent Publication No. 2005-300289